1. Field of the Invention
This invention relates to a clasp mechanism, and more specifically to a clasp mechanism which can be opened and closed and used for interconnecting two ends of a chain such as a necklace, bracelet, key holder and the like or for connecting the one end of the chain to another article.
2. Description of the Prior Art
Conventional clasps or snap-hooks of this type are disclosed in Japanese Utility Model KOKAI No. 4-3016, U.S. Pat. Nos. 4,319,384, 3,956,804 and 5,117,539 and the like. For example, as shown in FIG. 4, in a clasp or snap-hook 50, a main body 54 has a ring 52 in one unit so that one end of a jewelry chain 41 such as a necklace and the like is connected to the ring. Alternatively, a jewelry piece 40 can be directly connected to the ring 52. A curved hook 53 is provided to latch and unlatch an end-ring 41'. In some cases, this end-ring 41' is formed by the chain's other end itself, which is opposite to the one end connected to the ring 52. In other cases, the end-ring 41' may be connected to the jewelry piece 40 directly or to the other end of the chain 41. An arm 55 having a mating end 57 at its fore end is pivotally connected to the above main body 54 by means of a shaft 56.
A thumb piece 58 is formed at the back end of this arm 55 so as to be projected from the web of the main body 54. The arm 55 is constructed to be pivotable when the thumb piece 58 is pushed with a finger so that the mating end 57 of the arm 55 can be mated with the tip end of the hook 53. The arm 55 is urged by means of a spring 59 in the counter-clockwise direction of FIG. 4; in the outer peripheral direction with respect to the center C of an arc-shaped area surrounded by the hook 53 so that the mating end 57 is naturally engaged to the tip end of the hook 53 in the closed condition.
The clasp of this type can be used for latching an optional article. For example, a chain has, at its one end, a clip and the like for gripping a belt loop and, at its other end, the above clasp latching the article such as a pocket bell, key holder and the like. In this case, the clasp may be used for latching the chain to an end ring, which is directly attached to the article or to the article's case. Further, the clasp may be used for connecting the chain to another end-ring which is attached to the above clip and the like.
When the necklace having the conventional clasp 50 is put on, the thumb piece 58 is pivoted against the biasing action of the spring 59 so that the mating end 57 of the arm 55 is disengaged and separated from the tip end of the hook 53 in the clockwise direction of FIG. 4; in the direction toward the center of the hook 53. Thus, an encirclement which has been formed with the mating end 57 and hook 53 is in turn opened. Then, the hook 53 is inserted, from its tip end, into the end-ring 41', which is usually provided at the chain's other end of the chain 41 of a jewelry piece 40 such as a necklace, thereby the end-ring 41' can be latched to the hook 53. Next, by releasing the finger from the thumb piece 58, the arm 55 is pivoted by the biasing action of the spring 59 in the counter-clockwise direction of FIG. 4; in the outer peripheral direction with respect to the center C of the arc-shaped area surrounded by the hook 53. This pivotal movement is stopped when the mating end 57 of the arm 55 is mated with the tip end of the hook 53 so that the arm is returned to the initial position in the closed condition. Thus, wearing of the necklace is finished.
Generally, the clasp 50 of the above chain 41 has a small size with the length of 10 to 15 mm and the thumb piece 58 of the arm 55 is quite small so as to project from the web of the main body 54 with the height of about 1.5 to 2.0 mm. Accordingly, in manipulation for attachment and detachment of the jewelry piece, it is impossible with one hand that the thumb piece 58 is pivoted while the main body 54 is pinched. Therefore, while both side surfaces of the main body is pinched with the finger-tips of one hand, the pivotal movement of the thumb piece 58 is effected by hooking a finger-nail of the other hand so that the mating end 57 of the arm 55 is disengaged and separated from the tip end of the hook 53 toward the center. While this condition is remained by maintaining the application of the force to the thumb piece 58 with the finger-nail of the other hand, the tip end of the hook 53 should be inserted into the end-ring 41', which is chain's one end of the jewelry piece 40 or provided at the other end of the chain or at the optional article. Accordingly, the manipulation for attachment and detachment of the jewelry piece is not only complicated but difficult.
In both cases of detachment and attachment, while the main body 54 is pinched with the finger-tips of one hand, the thumb piece 58 is hooked by the finger-nail of the other hand. However, since this operation should be performed under the condition that user's arms are put around user's neck, the manipulation for attachment and detachment of the jewelry piece is particularly complicated.
Further, it is not easy to pinch the main body 54 with the finger-tips of the one hand while the application of the force to the quite small thumb piece 58 is maintained with the finger-nail of the other hand. Precisely, since it is difficult to maintain the open condition that the mating end 57 of the arm 55 is disengaged and separated from the tip end of the hook 53, the manipulation for attachment and detachment of the jewelry piece should be tried many times.